Salsa20 Implementation: Sum of 2 Words with Carries SuppressedSecurity of Salsa20 with some known...
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Salsa20 Implementation: Sum of 2 Words with Carries Suppressed
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I'm working on the 2nd part of the Salsa20 spec, and I want to implement a closure for the exclusive-or of two words(u32). The author defines the operation as the sum of two words with carries suppressed, but what does "carries suppressed" mean. Then I come across some summation notation:
$u=sum_i2^iu_i$
What does the variable "i" mean in this context exactly? I understand summation notation and the index variable, but the context of the spec doesn't elaborate enough for me to know what "i" indexes.
I realize this all may be very rudimentary, but I am a programmer first.
modular-arithmetic xor salsa20
edited 1 hour ago
DannyNiu
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asked 3 hours ago
whole_lotta_coinswhole_lotta_coins
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add a comment |
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I'm working on the 2nd part of the Salsa20 spec, and I want to implement a closure for the exclusive-or of two words(u32). The author defines the operation as the sum of two words with carries suppressed, but what does "carries suppressed" mean. Then I come across some summation notation:
$u=sum_i2^iu_i$
What does the variable "i" mean in this context exactly? I understand summation notation and the index variable, but the context of the spec doesn't elaborate enough for me to know what "i" indexes.
I realize this all may be very rudimentary, but I am a programmer first.
modular-arithmetic xor salsa20
edited 1 hour ago
DannyNiu
1,2441628
asked 3 hours ago
whole_lotta_coinswhole_lotta_coins
132
New contributor
whole_lotta_coins is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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$begingroup$
I knew it! Thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
add a comment |
$begingroup$
I'm working on the 2nd part of the Salsa20 spec, and I want to implement a closure for the exclusive-or of two words(u32). The author defines the operation as the sum of two words with carries suppressed, but what does "carries suppressed" mean. Then I come across some summation notation:
$u=sum_i2^iu_i$
What does the variable "i" mean in this context exactly? I understand summation notation and the index variable, but the context of the spec doesn't elaborate enough for me to know what "i" indexes.
I realize this all may be very rudimentary, but I am a programmer first.
modular-arithmetic xor salsa20
edited 1 hour ago
DannyNiu
1,2441628
asked 3 hours ago
whole_lotta_coinswhole_lotta_coins
132
New contributor
whole_lotta_coins is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I'm working on the 2nd part of the Salsa20 spec, and I want to implement a closure for the exclusive-or of two words(u32). The author defines the operation as the sum of two words with carries suppressed, but what does "carries suppressed" mean. Then I come across some summation notation:
$u=sum_i2^iu_i$
What does the variable "i" mean in this context exactly? I understand summation notation and the index variable, but the context of the spec doesn't elaborate enough for me to know what "i" indexes.
I realize this all may be very rudimentary, but I am a programmer first.
modular-arithmetic xor salsa20
modular-arithmetic xor salsa20
edited 1 hour ago
DannyNiu
1,2441628
asked 3 hours ago
whole_lotta_coinswhole_lotta_coins
132
New contributor
whole_lotta_coins is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 1 hour ago
DannyNiu
1,2441628
asked 3 hours ago
whole_lotta_coinswhole_lotta_coins
132
New contributor
whole_lotta_coins is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 1 hour ago
DannyNiu
1,2441628
edited 1 hour ago
DannyNiu
1,2441628
edited 1 hour ago
DannyNiu
1,2441628
1,2441628
asked 3 hours ago
whole_lotta_coinswhole_lotta_coins
132
New contributor
whole_lotta_coins is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 3 hours ago
whole_lotta_coinswhole_lotta_coins
132
asked 3 hours ago
whole_lotta_coinswhole_lotta_coins
132
132
New contributor
whole_lotta_coins is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
whole_lotta_coins is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
whole_lotta_coins is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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I knew it! Thank you.
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– whole_lotta_coins
3 hours ago
add a comment |
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I knew it! Thank you.
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– whole_lotta_coins
3 hours ago
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I knew it! Thank you.
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– whole_lotta_coins
3 hours ago
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I knew it! Thank you.
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– whole_lotta_coins
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1 Answer
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The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered 3 hours ago
forestforest
4,2161540
$endgroup$
1
$begingroup$
Again, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
$begingroup$
That's right, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
add a comment |
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1 Answer
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1 Answer
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$begingroup$
The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered 3 hours ago
forestforest
4,2161540
$endgroup$
1
$begingroup$
Again, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
$begingroup$
That's right, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
add a comment |
$begingroup$
The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered 3 hours ago
forestforest
4,2161540
$endgroup$
1
$begingroup$
Again, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
$begingroup$
That's right, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
add a comment |
$begingroup$
The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered 3 hours ago
forestforest
4,2161540
$endgroup$
The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered 3 hours ago
forestforest
4,2161540
edited 6 mins ago
answered 3 hours ago
forestforest
4,2161540
answered 3 hours ago
forestforest
4,2161540
answered 3 hours ago
forestforest
4,2161540
4,2161540
1
$begingroup$
Again, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
$begingroup$
That's right, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
add a comment |
1
$begingroup$
Again, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
$begingroup$
That's right, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
1
1
$begingroup$
Again, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
$begingroup$
Again, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
$begingroup$
That's right, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
$begingroup$
That's right, thank you.
$endgroup$
– whole_lotta_coins
3 hours ago
add a comment |
whole_lotta_coins is a new contributor. Be nice, and check out our Code of Conduct.
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I knew it! Thank you.
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– whole_lotta_coins
3 hours ago